Fall Fire for Effective Management: Is There a Seasonal Affective Disorder in Prescribed Fire?

Over the years, I have noticed several intriguing responses in natural communities to seasonal variations in prescribed fire. I've discussed this issue with many folks, have initiated several interesting, though largely unsatisfying, email strings on the subject and wrote an essay on the subject in a recent Missouri Natural Areas Newsletter. Through this process, I have found that the increasing utilization of spring burning, as opposed to the more historically relevant application of autumnal anthropogenic burning, is primarily driven by convenience rather than ecological soundness. And, that the assumptions underlying the prescription of spring fire (that either spring fire is harmless or that it is at least better than no fire at all) are potentially more wishful than accurate. Having observed significant losses in plant diversity and subsequent increases in weedy shrubs like sumac and blackberries in areas where spring fire has reigned supreme, my concern has only grown. Steve Buback (Natural History Biologist for the Missouri Department of Conservation), sharing my concerns, suggested we investigate the matter via a summary of the pertinent literature on the subject and present the summary at the Missouri Natural Resource Conference. So, that is what we are doing. On Friday, February 5, 2016 Steve Buback and I will be presenting a talk on the effects of spring and summer prescribed fire compared to fall and winter prescribed fire.

On the surface this appears to be a dense or debatable topic. However, after an exhaustive review of the literature, I was surprised to find that it really isn't. It is quite simple really. Given this, Steve and I agreed to post the literature summaries in advance. We are hoping a few people will help catalyze any questions/discussion via this forum and thereby help us to be better prepared for Q&A after the presentation. We are also hopeful that this little bit of publicity will get more folks in attendance, since the talk is on Friday (last day of the conference) and the title isn't horribly provocative.

So, I'll start the talk with a rundown of why people used to burn and why we burn now. Basically modern burning (in North America, mind you) falls into two camps; 1) managing rangeland for cattle production with a heavy bias for grasses and 2) to promote and/or support biodiversity. There may also be a tad of fire use to promote forestry here and there. Because most prescribed fire in Missouri is done through public and private conservation agencies, most of it is directed toward promoting and/or supporting biodiversity; a rich assemblage of plants, animals and all creatures great and small.

Unfortunately, I could find zero published results on the effects of seasonality of fire in woodlands and forests. All of the literature involves prairie habitats and even then it is sparse. The phenomenon shouldn't be much different, and if it is different, one would expect to see more exaggerated results in woodlands and forests since there is a higher ratio of C3 graminoids and forbs to C4 grasses in woodland and forests: the effect we are concerned about. Here are the results of the studies directly testing hypotheses of seasonality on plant community structure and composition followed by a summary/synthesis: Towne and Kemp 2003 – 8 year study using
annual fire (previous 3-4 year interval)

Weeds as defined by Aldous (1934): “There
are several species of forbs, or broad-leafed plants. In pastures most of these
are considered as weeds and will be designated as such. These forbs fluctuate
in abundance from year to year. The most abundant ones include:

-perennial
ragweed (Ambrosia
psilostachya)
[C=3]

-many-flowered
aster (Aster
ericoides)
[C=5]

-pasture
sage (Artemisealudoviciana)
[C=3] [

-whorled
milkweed (Asclepiasverticillata)
[C=2]

-prairie
cat’s-foot (Antennarianeglecta)
[C=4]

-Missouri
goldenrod (Solidagomissouriensis)
[C=6]

-stiff
goldenrod (Solidagorigida)
[C=5]

-blue-eyed
grass (Sisyrinchiumcampestre)
[C=5]

-wild
flax (Linumtexanum)
[C=5]

and
about a half dozen other species of minor importance.”

Howe 1994 – early flowering vs. late
flowering in experimental prairies in WI

-In
terms of resprouts, new
sprouts and seed production in long term study

-spring burns showed most dramatic increases
overall (worst option)

-fall
burns showed most decrease (best option)

-winter was second best option

-summer was third best option

Part 2. Fire Intensity (backfires vs. headfires)(no
summer component)

-spring
backfires resulted in higher density of stems than

fall or winter backfires or head fires

-backfires
and headfires in
all seasons but winter and fall

resulted in increased sumac

-fall
backfires resulted in zero population growth

-winter
backfires resulted in the only decrease

Given the long-term results, the lower
number of stems and seeds produced, the stable population growth and
suitability to herbaceous grass and forb diversity and productivity (from other studies), low
intensity fall backfires provide for the greatest biodiversity and ecological
function.

The studies don't offer anything as judgmental as "spring fire bad, fall/winter fire good/better", but rather a "spring, winter, fall, summer fire different" stance. In fact, none of the papers pushed or really even addressed the biodiversity loss. Because it was there and blatant, and because it is the question at hand, I have put a spotlight on it. I've always thought summer burning was a bad idea, but have learned through this process that if you had a C4 grass dominated restoration (as there are many such) a summer fire could be very beneficial.

That said, despite a thorough search and tons of asking around there do not appear to be any studies to the contrary; just nearly a century of research demonstrating the same phenomena.

Yes. Unfortunately, none of the studies looked at population dynamics or reported much in the way of effects on individual species. So we are forced to assume that the decrease in productivity corresponds to decreases in diversity (which it kind of has to) and richness (which it may not, but probably does). Some one really needs to directly test the hypothesis that spring fire decreases C3 graminoid and forb diversity and richness.

It is my understanding that the authors of the Konza based research in my post are governed or heavily influenced by the agriculture school as KSU and that they are careful not to shout too loudly about these types of things. A good friend of mine knows Gene Towne really well and has said as much. In fact, because of the Towne and Craine paper, Towne was "let go" from Konza after something like 30 years of employment there for suggesting that spring fire was potentially harmful. He had been trying to say it for decades (thus his earlier work) but he was more or less silenced by the system. I'm glad he finally got the word out, but sad he lost his job over it and that Konza lost a really good manager. It is all rather scandalous.

I look forward to the presentation later this week. Based on the studies reviewed and your conclusions, I am wondering why you focus specifically on fall burning rather that using the term dormant season more generally. The studies reviewed and your conclusions generally seem more consistent with the term 'dormant season.' Late September and early October are fall of course, but many herbaceous species are still non-dormant at these times.

Also, there has been some literature on burn season in long-leaf pine savanna communities. I realize it's not Ozark woodlands, but I figure you'd be interested if you aren't already familiar with this literature. This recent issue of the Southern Fire Exchange newsletter discusses and includes links to a few recent fire seasonality studies that do address fire seasonality effects on under story vegetation. http://www.southernfireexchange.org/newsletters/v5-5.pdf

Thanks for your comments, Quinn. Indeed, "dormant season" is a more apt and direct phrasing. Because they used "fall" in most of the papers, I stuck with it. But, the knowledge that winter burning appears to be as, if not nearly as, beneficial as "fall", "dormant season" is a nice summary term. I'll use dormant season from now on given the clarity it does provide to the topic.

I've read several papers involving fire in Long Leaf Pine communities. I've gleaned that seasonality is a very different thing in the deep south than it is for the Midwest; with very unique communities defined/initiated sometimes by growing season fires. I think people often confused the kinds of results reported from the south as being possible in the Midwest; proof to me that regional systems should dictate the application of fire. I'm looking forward to seeing your talk on invasives Tan-Tar-A.

Enjoyed reading this summary! Since I had the time right now, thought I would provide you with some of my thoughts and comments as I was reading the post. This is just a perspective as to what someone in the audience could be thinking as you present the material. By no means do I have a strong background in prescribed burning, nor the mid-western flora anymore. I had to break up my overall response into many replies since it was too big to publish it at one time.So here goes:

Comments and questions on your first section before summary of papers:“Through this process, I have found that the increasing utilization of spring burning, as opposed to the more historically relevant application of autumnal anthropogenic burning”• So how long ago did this ‘transition period’ from fall to spring burn occur?“Having observed significant losses in plant diversity and subsequent increases in weedy shrubs like sumac and blackberries in areas where spring fire has reigned supreme, my concern has only grown.”• Yes, its obvious but the negative results of spring fires seem to be LOSS of plant diversity and INCREASE in weedy shrubs (sumac and blackberries)“I'll start the talk with a rundown of why people used to burn and why we burn now.”• I know this is a summary of papers and presentation, but I am thinking what about ‘natural’ wildfires. When do they usually occur or what season? What is the observed result of a natural wildfire during a specific season on plant diversity or on weedy woody species? I would guess the same but do I really know?

Here is the next part:Comments and questions on summary of papers and data:Towne and Kemp 2003o “woody species showed no change (low density to begin with)” What species? Are they ‘weedy shrubs’?

Towne and Craine 2014o “grass biomass remained unchanged from autumn, winter and spring burns” Are these C3 or C4 or assumed just a mixture of each?o “spring burns reduced biomass by 50%” Did the forbs increase in autumn and winter then”o “spring burns had increase in 5 species (average C-value = 4.7)” Just curious as to what specieso “winter and fall saw increase in 6 species (average C-value=6.2)” Just curious as to what species

Howe 1994 o “spring fire hurts early perennials and encourages late perennials/summer fire hurts late perennials and encourages early perennials”o Do we consider any of these perennials as ‘weedy species’o Do early perennials or late perennials have more of a significant benefit when it comes to plant diversity in this specific area? I guess what I am saying is if you had to choose over late or early flowering perennials what one would you chose and why?

Comments and questions on your summary and ‘put simply’:“Others show that late spring and growing season fires increase woody plants like sumac, blackberries and dogwood.”o Sumac was highlighted in the paper summaries though not blackberry and dogwood?o Also what species of blackberry and dogwood are we talking about?“after forbs and C3 grasses break dormancy (late February to early March) their rates of mortality increase with the lateness of burning season”o What about perennial forbs and Carex spp. according to T&C, 2014, and early flowering perennials according to Howe “Spring fire decreases C3 grasses and forbs, favors C4 grasses and increases shrubby species recruitment and densities (carries high potential of net loss to biodiversity)”o The only data presented in the paper comments relating to ‘shrubby species’ was H,H,W,2011on sumac and T&K, 2003 that stated there was ‘no change’ even though there was low density to begin with.

Hi I'm a forest ecologist by training and I have some questions. Why have people been so determined to burn in the spring? Is it logistics of burning in that season or is it an attempt to kill woody species when they are breaking dormancy? I know that there has been a switch to growing season burns in upland forest ecosystems in an attempt to kill red maple and others in the understory.

How are dormant season burns historically relevant? Do you mean that they were the practice in the past or is there literature somehowing constructing historical fire regimes? How did often and when did native Americans burn?

Thanks for your questions. I've questioned many of the fire management folks (in Missouri, at least) and they all say that fire behavior is logistically more convenient in the spring. And, so folks say the fall/winter fires disrupt deer hunting season. Neither reason has anything to do with ecological dynamics.

There are many historical eyewitness accounts of native American fire practices from explorers, settlers and scientists. With very few exceptions, they documented these fires in journals with fall/winter dates and/or make comments like "their practice of burning after the first frost/after leaves drop".

A colleague of mine knows an Environmental History professor that has been poring over old medical doctor's journals from east-central Kansas; early to mid 1800's. These doctors documented daily weather and included native American fires. They are almost exclusively Oct-Nov.

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